When setting up Giveaway options, we are now auto-filling the most 4 common sizes. We find a number of first time race directors not quite sure what to put in, and most races have these sizes anyway. Of course, you can edit these, add other sizes and re-order them.
Longer term, we plan on introducing the ability for each runner to store their preferences for T-Shirt size – so they can pick these standard sizes and enable “one click” registration later this year.